1. Field of the Invention
The present invention relates to a transfer sheet suitable for making ink ribbons for transfer printers, a method of manufacturing the same, and a transfer printing method.
2. Description of the Related Art
FIG. 2 is a typical view of assistance in explaining a conventional transfer sheet and a method of manufacturing the same.
A conventional transfer sheet 20 in the form of an ink ribbon (JP-B No. 6-96307) by way of example comprises a ribbon (base sheet) 21, a plurality of ink regions each of a plurality of color ink regions (yellow, magenta and cyan ink regions), (thermal transfer layers) 22 (22Y, 22M, 22C), and color lines (identification marks) 23 of colors of the color ink regions 22, extending perpendicularly to the length of the ink ribbon.
The transfer sheet 20 is manufactured by a suitable method, such as a gravure printing method, using printing cylinders 201, 202, 203 and 204 each having a circumference three times the length of the ink regions. First, a Y transfer region 22Y is printed by using the yellow (Y) printing cylinder 201, an M transfer region 22M is printed by using the magenta (M) printing cylinder 202, and a C transfer region 22C is printed by using the cyan (C) printing cylinder 203, Finally, the mark printing cylinder 204 prints the identification marks 23.
This method of manufacturing the conventional transfer sheet is not efficient because the transfer layers are printed one by one by using the Y, the M and the C printing cylinder. The efficiency of this method may be improved by using a printing cylinder provided with a plurality of transfer layer printing plates, i.e., multiple plate printing cylinder.
Transfer layers of an ink ribbon printed by using a printing cylinder provided with a plurality of transfer layer printing plates differ subtly in thickness from each other because of dimensional errors in the transfer layer printing plates. When such an ink ribbon is used for printing (transfer printing), colors appear in hues different from expected hues. When a sublimation transfer method capable of full-color image transfer is used, different pictures differ from each other in the gray hue of highlights and middle tone areas.
In general, transfer printers use a plurality of ink ribbons, such as a three-color type of ribbon (Y, M, C), a four-color type of ribbon (Y, M, C, Bk), a ribbon with a protective layer (Y, M, C, OP) or a ribbon with high density.
In a conventional transfer printer, a cassette which contains an ink ribbon, has a detection hole corresponding the ink ribbon for determining the type of the ink ribbon (JP-A No. 64-27981). When the cassette is inserted into the transfer printer, the detection hole is detected by a suitable mechanical measure. Another cassette may have a reflection mark representing the type of a contained ink ribbon, and the reflection mark is detected by a sensor for determining the type of the ink ribbon (JM-A No. 3-29367).
The third method is that a ribbon on which an ink ribbon is wound has a bar-code representing the type of the ink ribbon, and the bar-code is detected by the transfer printer.
However, the above three methods cause the increase of manufacturing costs of printers, because the printers need to be provided with particular mechanisms for detecting the hole, the reflection mark or the bar-code. In addition, the detection hole and the reflection mark should be changed in accordance with the corresponding ink ribbon, which leads cost increase.
Identification marks including information about the type of ink ribbon have been developed to solve the above problems. For example, identification marks representing colors whose number and width are changed in accordance with the type of media for determining the type of media (JP-B No. 6-96307) (JM-B No. 7-12004) (JP-A No. 9-10956).
In this case, however, the area of identification marks and the length of ink ribbon have been increased because of the increase of the number of the identification marks, and therefore the effective recording length and width of the ink ribbon have been shortened.